PHOTOCONDUCTIVE REACTION PRODUCT OF N -beta- CHLORETHYL CARBAZOLE AND FORMALDEHYDE

ABSTRACT

AND AN ELECTROPHOTOGRAPHIC PROCESS EMPLOYING THE SAME.   A xerographic plate including a resinous organic photoconductive composition obtained from the reaction between n-beta-chloroethyl carbazole and formaldehyde satisfying the formula:

7 United States-Patent i 1 Watarai et al.

[ 51 Nov. 6, 1973 PHOTOCONDUCTIVE REACTION PRODUCT OF N -BETA-CIILORETI-IYL CARBAZOLE AND FORMALDEIIYDE [75] Inventors; Syu Watarai,Tokyo; IIisatake Ono,

Asakashi, both of Japan [73.] Assignee: Xerox Corporation, Stamford,Conn.

[22] Filed: Aug. 23, 1971 [2]] Appl. No.: 174,272

[30] Foreign Application Priority Data 11/1966 Hoegl 96/l.5

3,232,755 2/1966 Hocgl ct al. lo/1.5

FOREIGN PATENTS ()R APPLICATIONS 4,221,875 10/1967 Japan 96/1.54,319,012 8/1968 Japan... 260/675 437,592 3/1968 Japan 96/l.5

Primary Examiner-Roland E. Martin, Jr. AttorneyJames .l. Ralabate et al.

[57] ABSTRACT A xerographic plate including a resinous organicphotoconductive composition obtained from the reaction betweenn-beta-chloroethyl carbazole and formaldehyde satisfying the formula:

and an electrophotographic process employing the same.

13 Claims, No Drawings- PHOTOCONDUCTIVE REACTION PRODUCT OF N -BETA-CHLORE'IIIYL CARBAZOLE AND FORMALDEI'IYDE BACKGROUND OF THE INVENTIONThis invention relates to a photoconductive material and, moreparticularly, to the use of such a material in electrophotography.

The xerographic process as originally disclosed by Carlson in US. Pat.No. 2,297,691 generally involves applying a uniform electrostatic chargeto a photoconductive insulating layer which makes up the surface of axerographic plate so as to sensitize it. The plate is then exposed to animage of activating electromagnetic radiation such as light, X-ray, orthe like, which selectively dissipates the charge in illuminated areasleaving behind charge in the non-illuminated areas to form a latentelectrostatic image. The image so obtained is then developed or madevisible by deposition of finely divided electroscopic marking materialon the surface of the photoconductive insulating layer'as a result ofwhich the marking material conforms tothe pattern of the latent image.Wherethephotoconductive insulating material is reusable, this visibleimage of finely divided or powdered marking material is then transferredto a second surface, such as a sheet of paper, and fixed in placethereon to form a permanent visible reproduction of the original. Where,on the other hand, a less expensive, non-reusable photoconductiveinsulating material is employed the toner particles may be fixed inplace directly on its surface with the consequent elimination of thetransfer step from the process.

In the earlier Carlson work coatings of 'anthracene, melted sulfur, andthe like, were employed as the photoconductive insulating materials.However, these materials were found to have low sensitivity and producedonly fair images at best under present standards. A

great deal of development effort has been extended in attempting toprovide improved photoconductive insulating'layers for xerographicplates resulting in the production of a number of organicphotoconductors such as, for example, polyvinyl anthracene;2,5-bis-(p-amino phenol) -l ,3,4-oxadiazole;- polyvinyl carbazole andothers. Another major area of xerographic. plate. development involvesthe binder plate inwhijch finely divided photoconductive material suchas, cadmium sulfide,

cadium selenide, zinc sulfide, antimony sulfide, mercuric oxide, leadiodide,lead sulfide, lead telluride, and

other materials are dispersed in .a film-forming insulating binder tomake up the photoconductive insulatingalloys in the amorphous form, asdescribed in U.S. Pat.

No. 2,970,906 to Bixby have been found to be very successful from thecommercial point of view because of the fact that they can be made invery smooth layers, they're reusable and can produce high resolutionimages and are fairly sensitive to visible light and X-ray radiation.Mechanically, this preferred xerographic plate is fairly soft andeventually suffers surface degradation from abrasion with developingmaterial after the production of 50,000 to'l00,000 copies. In addition,the amorphous form of selenium is not as stable so that when platesincluding this type of selenium photoconductive layer are exposed toheat orcertain solvent vapors they frequently are converted toinoperative crystalline forms of selenium. Though this preferredelectrophotographic material suffers from these drawbacks, the amorphousselenium xerographic plate is the plate of preference in this-fieldbecause other photoconductors such as the photoconductive aromaticpolymers and binder plates described supra generally have lowsensitivity, lack of reusability, relatively low abrasion resistance,rough surface characteristics and similar deficiencies. In addition,many of these materials can be sensitized only by negative and not bypositive corona discharge techniques, that is, they are not ambipolar.Since negative corona discharge generates much more ozone than positivecorona and since it is much more difficult to control negative coronadischarge so as to uniformly charge the photoconductive SUMMARY v OF'THE INVENTION It is, therefore, an object of this invention to provide anovel xerographic plate devoid of the above noted disadvantages.

Another object of this invention is to provide a reusable xerographicplate having spectral sensitivity that extends over a wide range.

Still another object of this invention is to provide a reusablexerographic plate having high thermal stability and resistance tosolvents.

Yet another object of this invention is to provide a xerographic platewhich is resistant to abrasion and which is mechanically strong.

Yet'another object of this invention is to provide a ClCHzCI-I:

- ism This organic photoconductive material is found to possessexcellent xerographic properties when compared,

for example, to an n-ethylcar-bazole-formaldehyde resin. Otherconventionally available photoconductive materials unlike the compoundof the instant invention even though having relatively low molecularweights with an intrinsic viscosity of 0.089 dl/g (measured inn-methyl-2-pyrrolidone at 30C) are insoluble in toluene, dioxane,tetrahydrofuran, etc. and only soluble in polar solvents of high boilingpoints. They are, therefore, extremely difficult to apply on a supportas a coating and, therefore, are not practical for employment inelectrophotographic plates.

The organic photoconductive material of the present invention issynthesized by heating n-beta-chloroethyl carbazole the synthesis ofwhich is well known and may be found, for example, in Nippon KagakuZasshi, Volume 85, 1964, page 880, and formaldehyde in the form ofparaformaldehyde, formalin, or trioxane, etc. in an organic solvent, forexample,'dioxane or tetrahydrofuran in the presence of anacid catalyst.More specifically, 23 grams of n-bet a chloroethyl carbazole and 3 gramsof paraformaldehyde are dissolved in 200 ml of dioxane and 1 gram ofconcentrated sulfuric acid is added to the resultant solution. Themixture thusobtained is heated at a temperature of 90C for 4 hours withagitation and then poured into 3.1 liters of vigorously agitatedmethanol to obtain a white precipitate. The precipitate is separated byfiltering and dissolved in 200 ml of tetrahydrofuran and the solution soobtained is poured into methanol to obtain a refined precipitate. Theweight of the precipitate after drying is found to be 20.2 grams. Themolecular weight of the resin obtained in this manner is found to be14,000 by the vapor pressure repression method. The organic compoundthus obtained is solution coated on a conducting support such as a metalsheet, paper sheet, or plastic film treated to impart conductivity to athickness of up to 80 microns asa dry layer or preferably 2 to 20microns. A suitable plasticizer may be employed to improve flexibilitysuch as a chlorinated paraffin. The amount of the plasticizer added tothe polymer may range from to 100 weight percent based on-the weight ofthe polymer- In addition, the light sensitivity may be improved byincorporating well known sensitizers. Excellent results have beenobtained if the amount of the sensitizer added is less than 10 by weightof the electrophotographic composition.

The electrophotographic layer so prepared if sufficiently dry is foundto be substantially free from residual solvent and, therefore, capableof being uniformly charged in the dark by a corona discharge process,exposed to form a latent electrostatic image, and subsequently developedemploying well known developing techniques such as, for example, cascadedevelopment or a liquid developing process. Where it is desirable toemploy the cascade developing process, the developed image may be fixedby slightly heating the developed toner image or placing the toner imagein the vapor of an organic solvent capable of dissolving the resincomposition in the toner.

Any suitable coating technique for forming the photoconductive film ofthe present invention may be employed. Typical methods of coatinginclude: flow coating, bar coating, dip coating and Mayer rod drawdown.It should be understood, however, that whatever method is employedtoeither coat or form the organic photoconductive materials into thephotoconductive film of the present invention uniformity of thicknessand surface smoothness ought to be controlled so that they conform tothose acceptedelectrophotographic standards well known in the art. Thecoating of the photoconductive material of the present invention shouldbe uniformly deposited in thicknesses specified to a tolerance of plusor minus and preferably to a tolerance of plus or minus 10% of nominalthickness. The surface smoothness of the photoconductive member of thepresent invention should be such that conventionally known particulatedevelopers having particle sizes from about 2 to 10 microns can bereadily removed therefrom.

Any highly insulative resinous film-forming binder may be employed inthe system of the present invention to formthe electrophotographic plateof the present invention. Typical insulating resin binders include:styrene/butadiene copolymers, polystyrenes, chlorinated-rubbers,polyvinyl chlorides, vinyl chloride/vinyl acetate copolymers,polyvinylidene chloride, nitrocelf lulose, polyvinyl acetate, polyvinylacetal, polyvinyl ether, silicone resins, methacrylic resins, acrylicresins,

' phenol resins, alkyd resins, and urea/aldehyde resins.

Any suitable electroconductive base may be employed in the system of thepresent invention. Typical such electroconductive bases include:metallic plates, fabricated of chromium, aluminum, brass, stainlesssteel, copper, zinc and alloys thereof; paper treated to acquireelectroconductivity; and plastic films fabricated of aluminized Mylar(polyethyleneterephthalate) or conductive polymers.

Any suitable plasticizer may be employed in practicing the system of thepresent invention. Typical plasticizers include: chlorinated paraffin,phosphate plasticizers, phthalate plasticizers, and chlorinatedbiphenol, among others.

Any suitable sensitizer may be employed in practicing the system of thepresent invention. Typical sensitizers include: 1 tetracyanoethylene,tetracyanoquinodimethane, chloranil, bromanil, alphanapthalquinone',anthraquinone, methylene blue,'crystal violet, and malachite green,among others.

Any suitable method of charging may be employed in practicing the systemof the present invention. Typical methods of charging include: electriccharging in a vacuum, corona charging, friction charging and inductioncharging more fully described in U.S. Pat. Nos.

2,934,649 and 2,833,930 respectively and roller charging more fullydescribed in U.S. Pat. No. 2,934,650..

Any suitable'method of exposure may be employed in practicing the systemof the present invention. Typical methods of exposure include: reflex,contact, holographic techniques, non-lens slit scanning systems, andoptical projection systems involving lens imaging of opaque-reflectionsubjects as well as transparent film originals.

Any suitable method of developing may be employed in practicing thesystem of the present invention. Typical methods of developing include:power cloud development more fully described in U.S. Pat. Nos. 2,725,305and 2,918,910; cascade development more fully described in U.S. Pat.Nos. 2,618,551 and 2,618,552; and touchdown development.

Any suitable method of fixing the developed image obtained in practicingthe system of the present invention may be employed. Typical methods offixing include: heat-pressure fusing, radiant fusing, combinationradiant, conductive and convection fusing, cold pressure fixing andflash fusing.

To further define the specifics of the present invention the followingexamples are intendedito illustrate and not limit the particulars of thepresent invention. Parts and percentages are by weight unless otherwisespecified.

EXAMPLE l parts by weight of n-beta-chloroethyl carbazoleformaldehyderesin and 5 parts by weight of chlorinated paraffin are dissolved in 50parts of toluene. The resultant combination is coated on an aluminumsheet to a thickness of 5 microns as a dry layer and dried. The coatedmember so obtained is positively charged in the darkness by a coronadischarge process at 6 KV, exposed through a transparent positiveilluminated by an adjacent l00-watt tungsten lamp source located 30 cmfrom the electrophotographic member for 0.5 seconds. The latentelectrostatic image so obtained is developed empolying a developercontaining a negatively charged toner to obtain a positive toner image.The developed toner image is fixed by slightly heating to obtain a clearfixed image.

EXAMPLE II 0.2 parts by weight of tetracyanoethylene is added as asensitizer to the liquid coating composition as prepared in Example 1before the coating is employed as an electrophotographic member. Thesample thus obtained is subjected to the same charging, exposing,developing and fixing steps as outlined in Example I to obtain a clearfixed image with the exception of employing an exposure time of 0.2seconds.

Although the present examples were specific in terms of conditions andmaterials used, anyof the above listed typical materials may besubstituted when suitable in the above examples with similar results. Inaddition to the steps used to carry out the process of the presentinvention, other steps or modifications may be used if desirable. inaddition, other materials may be incorporated in the system of thepresent invention which will enhance, synergize or otherwise desirablyaffect the properties of the systems for their present use.

Anyone skilled in the art will have other modifications occur to himbased on the teachings of the present invention. Thesemodifications areintended to be encompassed within the scope of this invention.

What is claimed is:

1. An electrophotographic member comprising a conductive supportsubstrate and superimposed thereon an organic photoconductive film saidfilm comprising an organic photoconductive composition satisfying theformula:

2. An electrophotographic member as defined in claim 1 furthercomprising a sensitizer.

3. The electrophotographic member as defined in claim 1 furthercomprising a plasticizer.

4. An electrophotographic member as defined in 5 claim ll furthercomprising an insulating binder resin. 5. An electrophotographic membercomprising a conductive support substrate and superimposed thereon anorganic photoconductive film said film comprising a solid organicphotoconductive composition satisfying the formula:

ClCH CI-I;

tool

CICHQCH:

as I b olb. applying a substantially uniform electrostatic charge in thedark to the surface of said film; and

c. selectively dissipating said charge by exposure of the chargedsurface of said film to activating electromagnetic radiation, thusforming a latent electrostatic image on the surface of said film.

10. The imaging process of claim 9, wherein the latent electrostaticimage is rendered visible by development with finely dividedelectroscopic marking material.

11. An electrophotographic process as defined in claim 5 wherein saidelectrophotographic member is sensitized said sensitizer being selectedfrom the group consisting of tetracyanoethylene,tetracyanoquinodimethane, chloranil, bromanil, alphanaphthoquinone,anthraquinone, methylene blue, crystal violet, and malachite green.

12. The process as defined in claim 5 wherein said electrophotographiccomposition further comprises a plasticizer said plasticizer beingselected from the group consisting of chlorinated paraffin, phosphateplasticizers and phthalate plasticizers.

13. The process as defined in claim 5 wherein said electrophotographicmember is cascade developed.

2. An electrophotographic member is defined in claim 1 furthercomprising a sensitizer.
 3. The electrophotographic member as defined inclaim 1 further comprising a plasticizer.
 4. An electrophotographicmember as defined in claim 1 further comprising an insulating binderresin.
 5. An electrophotographic member comprising a conductive supportsubstrate and superimposed thereon an organic photoconductive film saidfilm comprising a solid organic photoconductive composition satisfyingthe formula:
 6. The electrophotographic member as defined in claim 5further comprising a sensitizer.
 7. The electrophotographic member asdefined in claim 5 further comprising a plasticizer.
 8. Theelectrophotographic member as defined in claim 5 further comprising aninsulating binder resin.
 9. An electrophotographic imaging processcomprising a. providing an electrophotographic member, said membercomprising a conductive support substrate having superimposed thereoveran organic photoconductive film said film comprising a solid organicphotoconductive composition satisfying the formula:
 10. The imagingprocess of claim 9, wherein the latent electrostatic image is renderedvisible by development with finely divided electroscopic markingmaterial.
 11. An electrophotographic process as defined in claim 5wherein said electrophotographic member is sensitized said sensitizerbeing selected from the group consisting of tetracyanoethylene,tetracyanoquinodimethane, chloranil, bromanil, alpha-naphthoquinone,anthraquinone, methylene blue, crystal violet, and malachite green. 12.The process as defined in claim 5 wherein said electrophotographiccomposition further comprises a plasticizer said plasticizer beingselected from the group consisting of chlorinated paraffin, phosphateplasticizers and phthalate plasticizers.
 13. The process as defined inclaim 5 wherein said electrophotographic member is cascade developed.